Wavelength division multiplexing (WDM) is a technology multiplexing a number of optical carriers over a single optical fiber by using different wavelengths. The technique enables bidirectional communications over one strand of fiber as well as multiplication of capacity. Through WDM, an optical communication network can be formed to deliver high capacity and high availability communication for today's ever increasing bandwidth intense applications.
One central advantage of a WDM centric solution is simplification through elimination of optical/electronic (O/E) conversion. A WDM network may utilize wavelength switches (WSSes) and optical add drop modules (OADMs), which can be either fixed or mini reconfigurable OADMs (ROADMs) for networking, for example, through network architecture disclosed in U.S. patent application Ser. No. 13/420,416, entitled “Optical Network Architecture for Transporting WDM traffic,” U.S. patent application Ser. No. 13/484,115, entitled “Resilience in an Access Subnetwork Ring,” U.S. patent application Ser. No. 13/651,877, entitled “Service Edge Hub Device and Methods in an Optical Network Node,” dated Mar. 14, 2012, May 30, 2012, and Oct. 15, 2012 respectively, incorporated by reference herein. Comparing to conventional packet aggregation networks, network intelligence is decoupled from the network device carrying traffic and transferred to the boundaries of segment (e.g., to the lambda controller, discovery unit, and smart optical interfaces).
For the WDM centric solution to work, however, the boundaries of segment need to know detail network topology information to perform wavelength routing. The process of discovering the network topology is fundamental for network control and management. One example concerns the protection process where network topology is needed to identify the shared risk group (SRG) and to isolate network failures.
The network topology information can be obtained in network planning process. Yet, network topology of a WDM network changes during operations due to various reasons, such as network device/fiber failures.
Topology information required for network control and management consists of network devices and fiber connectivity between the network devices including port information. As an example, this means that the port number of a wavelength selective switch (WSS) that connects a fiber access ring must be known. Depending on the level of detail of the planning information, topology discovery can be used to verify or discover remote network elements and port information.
Known existing schemes for topology discovery are on the packet level and include:
SNMP discovery—The SNMP manager software (present in a discovery tool), queries the SNMP-enabled devices in the network. Based on these SNMP queries and replies, the manager then builds up the network map, complete with details on device location.
Active probes—In this approach, the discovery tool sends out light-weight “probe” packets through the network. The probe scans the network, and transmits device-related data back to the discovery module.
Yet, these conventional packet based approaches for topology discovery above are not directly applicable to WDM networks, since these approaches require software/hardware complexity at the network devices, so that the network devices can either passively respond to the queries made by the network control node, or actively report their existence to the network controller. These approaches also require proprietary mechanisms or standard network protocols (SNMP, IP, etc.) to be understood to achieve the full set of functionalities. For example, SNMP discovery requires that network devices have SNMP capabilities, which could be prohibitively expensive if equipped for every OADM. But more importantly, WDM networks is generally a layer-1 architecture that provides wavelength transport services between the clients and the network service equipment, which is transparent to upper layer protocols for complex network functions. Therefore, a discovery process for WDM networks should be performed on the wavelength level, and cannot rely on packet-level support.
In a WDM network, the network devices such as WSSes and OADMs have limited capabilities of providing local information relevant for building the topology map. The passive elements such as OADMs The passive elements such as OADMs are unable to either report their existence or respond to inquiries from higher-level network elements. For active elements such as WSSes or mini-ROADMs there will be operations, administration, and management (OAM) connectivity with the lambda controller for control purposes. However, limited information can be extracted from these network elements for topology mapping purposes.
Thus, it is desirable to discover WDM network topology automatically without solely depends on static network topology information obtained in network planning process or packet based topology discovery.